1. Field of the Invention
The present invention relates to improvement in performance, that is, increasing speed of rotation, reducing vibration, decreasing power consumption, and lowering costs, of a highspeed motor such as for example spindle motor, which is used in the disk drive of a computer peripheral memory device, or an audio-visual device, which has a digital disk as a medium, of office automation (OA) equipment or audio-visual (AV) equipment, and more particularly, to a highspeed motor stator structure, which is designed to increase the efficiency of a magnetic circuit, and to enhance motor performance.
2. Description of the Related Art
FIG. 1 is a cross-sectional view of a conventional outer rotor radial gap-type highspeed motor.
A conventional highspeed motor is of an outer rotor-type with radial gap. Because a stator yoke 3 is constituted by stacking up a required number of disks made of soft-magnetic steel sheets, which constitute a salient pole 6, there is a little space for winding. Therefore winding is not possible in a separate process using a bobbin or the like. Magnet wire is directly wound on the stator yoke 3 without using the bobbin and therefore a long time is required for winding process and there will be a possible deterioration of quality caused by damages on the wire. Magnetic force of a rotor magnet 7 acts principally in the radial direction, and the magnetic force in the direction of the shaft 10 is extremely weak. As has been disclosed in various applications, even when the center of the rotor magnet is placed above the center of the shaft 10, and axial magnetic force is increased, the axial magnetic force is still weak, and when a disk is mounted to the rotor and rotated at highspeed, it is difficult to maintain the initial position of the disk. In recent trend, decrease in cost of the equipment is especially intense, and there has been a change from ball bearings to metal bearings 11 with a view to increasing the rotating speed of the disk, and reducing bearing costs. This causes difficulty in preventing the rotor from floating and more effective methods have been demanded.
As means for solving these problems, there has been proposed a salient pole-type motor with axial gap (refer to Japanese Patent Application No. 9-306771) as shown in FIGS. 2A and 2B, in which the magnetic force of the rotor magnet and the orientation of the magnetic flux as a field magnet is in the same direction to increase the axial magnetic force of the rotor.
FIG. 2A is a cross-sectional view of a conventional highspeed motor of salient pole-type with axial gap similar to the present invention, and FIG. 2B is a perspective view of a stator of the motor.
As will be readily understood in FIGS. 2A and 2B, the salient poles 6 of the stator yoke 3 have surfaces protruding in both radial and axial directions oppositely to the rotor magnet 7 fixed on a rotor yoke 8. Therefore effective magnetic flux can be extracted in abundance, thus promoting enhanced characteristics. However, because the salient poles 6 are magnetically interconnected through only a base plate 1 without any magnetic circuits provided therebetween, the length of the magnetic path becomes long, and connection points become numerous, making it easy for magnetic resistance to increase, and making it impossible to further improve characteristics. To make the stator structure more compact, smaller in diameter, and higher in performance, the magnetic circuit must be made highly efficient by suppressing increase in the magnetic resistance thereof.
With the foregoing problems in view, it is an object of the present invention to provide, at low cost, a stator structure of a high-performance motor, which gives off lower temperature rise, strives for a more highly efficient magnetic circuit, and achieves lower power consumption at highspeed rotation, while at the same time striving to achieve a stable rotor position by preventing rotor float at highspeed rotation.
To solve for the above-mentioned problems, there is provided a highspeed motor comprising a stator including a stator yoke and coils each arranged on each of a plurality of salient poles on said stator yoke and a rotor rotatably arranged facing the salient poles of said stator by way of an air gap, stator yoke is constituted by a belt-shaped yoke forming ribbon, having a plurality of salient pole forming portions connected via magnetic connecting portions.
Further, the present invention is a directed to an highspeed motor comprising a stator including a stator yoke made of a soft magnetic material sheet and coils composed of magnetic wires wound on salient poles of said stator yoke; a rotor including a field magnet consisting of a permanent magnet so as to face said salient poles of said stator by way of an air gap and a shaft as the center of rotation in the center thereof; and a base plate having a bearing for rotatably holding said rotor in the center of said stator characterized in the stator yoke is constituted by winding a soft magnetic material sheet.
Further, the present invention is characterized in that there is provided on the opposite side of a salient pole of the stator yoke a protruding portion, which serves both to position and fix the stator.
Further, the present invention is characterized in that the height of the magnetic connecting portion for interconnecting salient poles of the yoke forming ribbon is less than one fourth of the height of a salient pole.
Further, the present invention is characterized in that the salient pole of the stator yoke is formed so that the width of the area facing the above-mentioned rotor is narrow on the motor shaft side, and becomes wider towards the outer circumference of the motor.
Further, the present invention is characterized in that the height of the salient pole of the stator yoke is formed so as to be higher on the side of the motor shaft, and to become lower towards the outer circumference of the motor.
Further, the present invention is characterized in that the above-mentioned stator yoke is fixed, via a bobbin wound with the above-mentioned coil, to the base plate, which supports a bearing of the above-mentioned rotor shaft.